Consider the following sulphur based oxoacids.

$$\mathrm{H}_{2} \mathrm{SO}_{3}, \mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{8}$$ and $$\mathrm{H}_{2}\mathrm{S}_{2} \mathrm{O}_{7}$$.

Amongst these oxoacids, the number of those with peroxo $$(\mathrm{O}-\mathrm{O})$$ bond is ________.

A 1.84 mg sample of polyhydric alcoholic compound 'X' of molar mass 92.0 g/mol gave 1.344 mL of $$\mathrm{H}_{2}$$ gas at STP. The number of alcoholic hydrogens present in compound 'X' is ________.

The number of stereoisomers formed in a reaction of $$(±)\mathrm{Ph}(\mathrm{C}=\mathrm{O}) \mathrm{C}(\mathrm{OH})(\mathrm{CN}) \mathrm{Ph}$$ with $$\mathrm{HCN}$$ is ___________.

$$\left[\right.$$where $$\mathrm{Ph}$$ is $$-\mathrm{C}_{6} \mathrm{H}_{5}$$]

The number of chlorine atoms in bithionol is __________.